Abstract— Precise speed control is an important
requirement for efficient industrial automation. Direct current
(DC) motors have been extensively used for this purpose. The
conventional method employs analog circuits to control the
speed of the DC motor by varying the voltage of the armature
while the field voltage is kept constant. In this paper, a digital
speed control of DC motor using pulse width modulation
technique was implemented by replacing analog circuit with an
Atmel AT89S52 microcontroller circuit. An experimentation of
the design showed that the DC motor can run forward
motoring, forward regeneration, reverse motoring and reverse
regeneration. This digital approach proved to have increased
precision and greater control efficiency. Thus, a centralized
control of several motors can also be achieved.
Index Terms—DC motor speed control, microcontroller,
pulse width modulation, quadrant choppers
I. INTRODUCTION
UTOMATION of industrial processes offers the benefits
of better quality, increased production and control, and
decreased costs. Several industrial automation processes
utilize electric motors for control functionalities. This
requires the electric motor to operate at different speeds and
in different modes. High starting torque and controllability
of Direct Current (DC) motors has led to their wide range
usage in industrial processes that require accurate and
precise speed control.
DC shunt motors are considered appropriate for most
industrial control due to their advantageous features. They
operate at approximately constant speeds. For the same
current input, the starting torques is not as high as in series
motors. To maintain an approximately constant speed from
no-load to full-load, the shunt regulator enables the required
speed control easily and economically. DC shunt motors
have wide range of applications which include driving
constant speed line shaft loads, lathes, centrifugal pumps,
machine tools, blowers and fans, and reciprocating pumps
[1]. They achieve higher accuracy, greater reliability, quick
response, and higher efficiency since there are no I2R losses.
A full four-quadrant control is possible to meet precise high-
speed requirement [2].
Manuscript received February 23, 2017; revised March 28, 2017.
A. U. Adoghe, S. O. Aliu, S. I. Popoola, and AAA. Atayero,
Department of Electrical and Information Engineering, Covenant University, Ota, Nigeria.
{anthony.adoghe, atayero} @covenantuniversity.edu.ng,
Over the years, various DC shunt motor speed control
techniques have been employed. In flux control approach,
the motor speed increases as the rate of flux decreases. The
rate of flux changes when the shunt current is varied using a
shunt field rheostat. Since the shunt current is relatively
small, the shunt field rheostat has to carry only a small
current which results in low I2R loss, such rheostat is small
in size. This method is therefore very efficient [3].
The rheostat control method is suitable when speeds below
the no-load speed are required. With a constant supply
voltage, the voltage across the armature is varied by
inserting a variable rheostat in series with the armature
circuit. For a constant load torque, the speed is
approximately proportional to the potential difference across
the armature [3]. However, this technique is inefficient,
expensive, and not suitable for rapidly changing loads. For
better improvement, a diverter can be connected across the
armature in addition to the armature control resistance.
The voltage control method may be multiple voltage control
or Ward-Leonard system. In multiple voltage control, the
shunt field is permanently connected to a fixed exciting
voltage but the armature is supplied with different voltages.
This is achieved by connecting the armature across one of
the several different voltages by means of suitable gear. The
intermediate speeds can be obtained by adjusting the shunt
field regulator. However, this method is not frequently used.
The Ward-Leonard method is used where an unusually wide
and very sensitive speed control is required. However, its
overall efficiency is low at light loads [3].
Prior to the advent of power electronics and
microcontrollers, it has been very difficult to realize variable
speed of DC motors in any application. Today, solid-state
electronic devices have become a better choice for DC
motor speed control [11]. These devices control the motor
speed by adjusting either the voltage applied to the motor
armature, the field current, or both [6]. Unipolar pulse width
modulation is suitable for cases where the reversal of motor
direction is not required. A bidirectional DC motor speed
control can be achieved using the H-bridge integrated
circuits controlled by a microcontroller [7].
In this paper, we design and implemented the digital speed
control of DC motor using pulse width modulation
technique. The analog circuit was replaced with an Atmel
AT89S52 microcontroller circuit. Similar to the traditional
approach, the field voltage was kept constant while the
armature voltage was varied. The switching action was done
by four-quadrant choppers which utilized Metal–Oxide
Semiconductor Field-Effect Transistors (MOSFETs). The
Digital Speed Control of DC Motor for
Industrial Automation using Pulse Width
Modulation Technique
Anthony U. Adoghe, Simisola O. Aliu, Segun I. Popoola, Aderemi A. Atayero, Members, IAENG
A
Proceedings of the World Congress on Engineering 2017 Vol I WCE 2017, July 5-7, 2017, London, U.K.
ISBN: 978-988-14047-4-9 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2017
motor was connected to the Optoisolator-MOSFET
circuitry. Optoisolators accepted the input signals from the
microcontroller and provide instructions to the integrated
circuit that controls the MOSFETs. The Microcontroller is
connected and programmed to work with a Liquid Crystal
Display (LCD) unit and a keypad.
The remainder of this work is organized as follows:
Section II gives the materials and explains the methods
employed; Section III presents the system implementation
and testing procedures; Section IV discussed and
summarized the results obtained.
II. MATERIALS AND METHODS
Correct design specification is required for efficient
system performance. The design parameters considered
include input voltage, output voltage, maximum current,
frequency of operation, voltage control steps, and direction
of rotation. The DC motor controller operates at 6 V/12 V
with a maximum current capacity of 5 A. The system
operates at a frequency of 50 Hz. The input AC voltage is
within the range of 150–270 V. A digital display is required
to show the exact value of the input and the output voltages.
Also, the current speed and direction of rotation should be
displayed. Switches control the desired voltages (6 V/12 V/
24 V), the speed range from 1 to 100 in steps of 1 and 5. The
direction can be either clockwise or anticlockwise.
The complete system consists of six (6) different units.
This include the power supply unit, the microcontroller unit,
optoisolator unit, the LCD display unit, the MOSFET
chopper unit, and the DC motor. This block diagram in
Figure 1 shows the interconnections of the various units.
Figure 1: Block Diagram of the System
A. The Power Supply Unit
The power supply is made up of the transformer, the
rectifier circuit, the filter circuit, and the regulator circuit.
The circuit arrangement is shown in Figure 2. Two
transformers are used to step down the AC voltage of 230 V
to 15 V. The diodes converts the input AC current into DC.
This is known as rectification. The rectified output is a
rippled DC which requires filtering. The ripples are filtered
using a capacitor arrangement. A positive voltage regulator
is used to control the output DC voltage.
Figure 2: Block Diagram of Power Supply Unit
Three different power supplies were used to supply
appropriate operating voltage to the microcontroller unit and
two DC motors respectively. A series connection of two
center-tap step down transformers of 15 V output voltage
each fives a total power rating of 30 V, 5 A. The 30 V
output of the transformer was fed into the bridge rectifier
circuit. The diodes employed in the rectifier circuit have a
forward bias of 0.7V each. A 12 V zener diode and 7805
voltage regulator IC control the DC output of the filter
circuit. The output voltage of the regulator circuit is 5 V that
is required for the operation of the microcontroller unit [13].
B. The Microcontroller Unit
A microcontroller is made up of a powerful processing
unit integrated with memory, and various input and output
interfaces, all on a single chip. The use of a microcontroller
reduced the size of the Printed Circuit Board (PCB) and the
cost of design.
The programmable microcontroller used in this work is
AT8952. The choice of this microcontroller is due its small
size and cheap price. It has a 4 KB of in-system
programmable flash memory, 1000 write/erase cycles, 128 x
8-bit internal Read Only Memory (RAM), two 16-bit
timer/counters, and six interrupt sources. It is also equipped
with full duplex UART serial channel, low-power idle and
power-down modes, watchdog timer, and dual data pointer
[10]. In addition, AT8952 has a high speed of program
execution and high processing capability. The interface and
the memory was adequate for the task at hand since it has to
learn only 35 single word instructions. The above-
mentioned requirements facilitate the choice of the AT8952
chip.
All the instructions for control functions are programmed
into the microcontroller. The 5 V DC output of the power
supply is connected to pin 40 of the microcontroller. The
microcontroller uses a pull down resistor connected to port
0, and a crystal oscillator of 11.0592 MHz in conjunction
with a couple of capacitors of 27 µF. The resistor and the
crystal oscillator were connected to pins 18 and 19 of the
microcontroller for stable oscillation as shown in Figure 3.
C. The LCD Display Unit
The unit is responsible for the digital display of output
information. The LCD was properly interfaced to the
microcontroller as sown in Figure 4. The data pins of the
LCD were connected to port 2 of the microcontroller.
D. The Keypad Unit
The keypad allows the user to input required instruction to
the microcontroller as predetermined. There are eight keys
on the keypad for different operations as shown in Figure 5.
The keypad switches were connected to port 1 of the
microcontroller. The possible operations include the
switching function, speed control function, the changing of
the output voltage, and the changing of direction of rotation
of the DC motor.
Proceedings of the World Congress on Engineering 2017 Vol I WCE 2017, July 5-7, 2017, London, U.K.
ISBN: 978-988-14047-4-9 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2017
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Figure 3: The Microcontroller Unit
Figure 4: Interfacing LCD with the Microcontroller
Figure 5: The Keypad Unit
A. The DC Motor
The DC motor is the output device that is varied by the
control switches. The speed of the DC motor is directly
proportional to the armature voltage and inversely
proportional to the flux. By maintaining a constant flux and
varying the armature voltage, the speed of the motor is
varied.
B. The Optoisolator Unit
The optoisolator was used to transmit signals or data
across an electrical barrier using a beam of light, and it
achieved an excellent isolation [12]. In this work, they were
used in the transfer of on-off control signals for switching
purposes and for circuit isolation. The second pins of all the
optoisolators were interconnected while the first pins were
connected to resistors. Interchanging the positions of the
pins and the optoisolators changes the direction of rotation
of the DC motor. The optoisolator supplied an input to the
microcontroller. The microcontroller processes the
information and display the appropriate output on the LCD
display unit.
C. The MOSFET Chopper Unit
A chopper is a DC to DC converter with a variable DC
voltage [9]. The MOSFETs acted as switches as shown in
Figure 6. They are employed to switch on and off the power
supply to the load for a certain time interval. This was
achieved by varying the firing angle. By so doing, the speed
of the DC motor was controlled.
D. Software
Keil µVision3 software, Express PCB, and Express SCH
were used for the programming, the layout design, and the
schematic design respectively. µVision3 is an Integrated
Development Environment (IDE) for code writing,
compilations, and debugging [14]. It comprised of a project
manager, a make facility, tool configuration, an editor, and a
debugger. Express PCB V5.6.0 and Express SCH V5.6.0
were used in this work. The codes were written in assembly
language. This language was preferred to a high-level
programming language because of speed, control, and
preference. The programs run faster since there is no need
for compilation of source codes. The programmer interacts
with the embedded system hardware directly.
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Vcc(6-24v)
gnd(6-24v)
Motor a
vcc1
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unregulated
(6-24v)
Motor b
gnd(6-24v)
Vcc
unregulated
(6-24v)
vcc2
gnd2
Vcc(6-24v)
a
c
b
d
Figure 6: The Chopper Circuit
Proceedings of the World Congress on Engineering 2017 Vol I WCE 2017, July 5-7, 2017, London, U.K.
ISBN: 978-988-14047-4-9 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2017
III. SYSTEM IMPLEMENTATION AND TESTING
The complete circuit was initially arranged on a bread
board and stage by stage testing was performed before it
was finally implemented on a PCB board. Thereafter, the
various components that made up the circuit of each unit of
the system were soldered in tandem to meet desired
workability.
Three voltage levels were achieved using the DC motor
controller. They are 6 V, 12 V, and 24 V with a maximum
current capacity of 5 A. The 12 V and 5 V outputs were
supplied to the switching circuit and the control circuit
respectively. In addition to the traditional power supply
circuit, a circuit called Switched Mode Power Supply
(SMPS) was used for efficient, secured voltage supply to the
microcontroller, eliminating possible fluctuations. This was
used to supply voltage to the various stages of the circuit
during the breadboard test. During the soldering phase, the
power supply was still used to test various stages before
they were finally soldered.
The main component in the control circuit is the
microcontroller, AT8952. The microcontroller was
programmed before physical implementation on the PCB
board. The ASM compiler used for debugging was the
mikrolingual complier.
Figure 7: Interconnections of the Power Supply Unit and the Control Unit
Other component parts of the control circuit include
current limiting resistors, filtering capacitors, rectification
diodes, crystal oscillators and voltage regulators as shown in
Figure 7. The switching circuit comprised of MOSFETs.
The arrangement of the optoisolators, zener diodes,
transistors, resistors, filtering capacitors, power buffers
(TIP41C) transistors was to amplify the current to a required
level needed to drive the MOSFETs and voltage regulators.
The LCD was connected to the system so as to monitor
and display the speed of the motor, the direction of the
motor (clockwise or anticlockwise) and its output voltage
(6V, 12V or 24V). The NHD-0216K1Z-NSW-BBW-L
model was selected because of the following features: new
haven display; 2 lines by 16 characters; version line; side
white LED; and low power [8].
At the final stage, all the circuit components were
carefully soldered on a PCB. The PCB was used instead of
veroboard because of its higher efficiency with little or no
short circuit between current paths. Also, the choice of PCB
made the circuit design compact, and ensured neatness by
eliminating the need for connecting wires. A local, cost-
effective copper etching technique was used. The circuit
design were done using Express PCB software as shown in
Figure 9. Hard copies were printed and pasted on copper
clads. Heat generated by electric iron was used to transfer
the circuit diagram pattern to the copper clad surface. The
uncovered portions of the copper clad were etched in Iron
Chloride. The appropriate components were carefully placed
in drilled holes for onward soldering. The electrical
components were soldered to form a complete circuit as
designed shown in Figure 8.
Figure 8: Complete System Circuitry
Figure 9: PCB Layouts of the Control Circuit
The circuits were separately tested to ensure that the
correct input and output values were obtained. This was
done using a multimeter. DC motors were tested with input
voltages of 6, 12, and 24 V. Keys assigned to different
functions were tested and the information such as the supply
voltage, speed of rotation, and direction of rotation was
monitored as displayed on the LCD as shown in Figure 10.
Figure 10: Result Display on the LCD
A digital multimeter was placed across the terminal of the
output of the LCD to test if what was displayed corresponds
to the readings on the digital multimeter. This was also
repeated for the input terminals. The readings were accurate
when compared to the digital multimeter readings. The
whole system was well packaged with good furnishing as
shown in Figure 11.
Proceedings of the World Congress on Engineering 2017 Vol I WCE 2017, July 5-7, 2017, London, U.K.
ISBN: 978-988-14047-4-9 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2017
Figure 11: The External Outlook of the System
IV. CONCLUSION
This work achieved a design and implementation of a DC
motor speed control for operating voltages of 6 V, 12 V, and
24 V with a maximum current capacity of 5 A. The control
mechanism enables efficient speed regulation with more
reliable functionalities even at large currents. The analog
circuit was replaced with an Atmel AT89S52
microcontroller circuit. Similar to the traditional approach,
the field voltage was kept constant while the armature
voltage was varied. The switching action was done by four-
quadrant choppers which utilized Metal–Oxide
Semiconductor Field-Effect Transistors (MOSFETs). The
operating characteristics of the motor can be altered using
the keypad. The DC motor operates in four operation
modes: forward generating; forward motoring; reverse
generating; and reversed motoring. The control information
is displayed via the LCD unit.
However, the application of four-quadrant chopper
control is limited to DC motors whereas AC motors have
extensive applications in industrial automation. Therefore,
future work should be done to achieve digital speed control
of AC motors.
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[2] Irvin M. Gottlieb, “Electric Motor and Control Techniques”, Jameco, 2nd Edition, Chapter 2, pp. 32-54.
[3] B.L. Theraja and A. K.Theraja, “A Textbook of Electrical
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[4] P.S. Bimbra, “ Power Electronics”, Delhi, Khanna Publishers, 2007.
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[10] M. A. Mazidi, J. G. Mazidi and R.D. McKinlay, “The 8051
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[11] M.D. Singh and K.B. Kanchandani, “Power Electronics”, Tata McGraw Hill, 2008.
[12] Texas Instruments, “MCT2, MCT2E Optoisolators SOES023
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[13] Fairchild Semiconductor, “3 Terminal 1A Positive Voltage Regulator:
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Proceedings of the World Congress on Engineering 2017 Vol I WCE 2017, July 5-7, 2017, London, U.K.
ISBN: 978-988-14047-4-9 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2017